1. Field of the Invention
The present invention relates to a proportional fluid control valve.
2. Description of Related Art
The flow of fluids is typically controlled by a fluid control valve(s). A conventional fluid control valve has a spool or other similar element that is movable between two positions. The spool is typically moved into one position by a solenoid and pushed back to the original position by a spring or another solenoid. The spool is in either one of two positions. Consequently, the flowrate through the valve is limited to the two positions of the spool. By way of example, a two-way valve is either open or closed, so that the flowrate through the valve is either at a maximum value or zero.
It is sometimes desirable to vary the flowrate in a fluid system. For example, insecticides are sometimes sprayed from a moving vehicle. As the vehicle is driven about a field, it may be desirable to limit the range of the spray so that insecticide does not fall onto a certain area. As another example, it may be desirable to vary the range of a water stream emitted by a sprinkler system so that the water more completely covers an area adjacent to the sprinkler heads.
To change the fluid flowrate, some fluid systems have a variable speed pump motor that is controlled by an electronic controller. The controller can be programmed, or receive manual inputs, to change the speed of the motor and the pressure of the pump. The change in pump pressure varies the fluid flowrate within the system. Variable speed pumps are relatively expensive and provide relatively inaccurate and unproportional control of the fluid flowrate, particularly if multiple valves and nozzles are used in the system.
Another method for controlling fluid flowrate is to incorporate a flow restrictor within the system. The flow restrictor may contain a valve that varies and restricts the flow of fluid in the system. By way of example, a sprinkler system may contain a cam driven flow restrictor valve that is attached to a moving sprinkler head. The restrictor valve incrementally closes and reduces the range of the water stream after each revolution of the sprinkler head. The control of a mechanical flow restrictor is limited to the particular assembly installed. Any variation in the flowrate typically requires the adjustment of a spring or other mechanical element. This requires the operator to be available and in a position to adjust the restrictor valve. This may be undesirable, particularly if the operator must also perform another function such as driving a vehicle that sprays insecticides. It would be desirable to have an electronically controlled fluid valve that provides proportional control of a fluid.